Electrically powered vehicles such as electric vehicles and hybrid vehicles have attracted a lot of attention as environmentally friendly vehicles. These vehicles incorporate a motor for generating a driving force for running, and a rechargeable power storage device for storing power supplied to the motor. A hybrid vehicle refers to a vehicle incorporating a motor as well as an internal combustion engine as a power source, a vehicle incorporating a power storage device as well as a fuel cell as a direct-current power supply, and the like.
As with an electric vehicle, a hybrid vehicle having a vehicle-mounted power storage device that can be charged from a power supply outside of the vehicle is known. For example, a so-called “plug-in hybrid vehicle” is known in which a power storage device can be charged from a power supply of an ordinary household by connecting a power supply outlet provided in the house to a charging inlet provided on the vehicle by a charging cable.
Contactless power transmission without using a power cord or a power transmission cable has been receiving attention in recent years as a power transmission method. Power transmission using electromagnetic induction, power transmission using a microwave, and power transmission by a resonance method are three dominant techniques known for the contactless power transmission.
Japanese Patent Laying-Open No. 2002-272134 (Patent Document 1) discloses a contactless power feeding apparatus using electromagnetic induction. This contactless power feeding apparatus includes a high-frequency power supply unit, a primary lead, a power receiving coil, a resistance detection circuit, and a frequency control unit. The high-frequency power supply unit generates high-frequency electric power. The primary lead converts the high-frequency power generated by the high-frequency power supply unit to a high-frequency magnetic flux. The power receiving coil receives the high-frequency power in a contactless manner from the primary lead by the action of electromagnetic induction, and supplies the same to a load. The resistance detection circuit detects a resistance component of the load. The frequency control unit controls the frequency of the high-frequency power generated by the high-frequency power supply unit, in accordance with the resistance component of the load detected by the resistance detection circuit.
According to this contactless power feeding apparatus, the frequency of the high-frequency power generated by the high-frequency power supply unit is controlled in accordance with the resistance component of the load detected by the resistance detection circuit, so that the power factor of the high-frequency power output from the high-frequency power supply unit can be substantially close to “1”. According to this document, this increases efficiency of power consumed in the load relative to apparent power (voltage×current) supplied by the high-frequency power supply unit, thereby attaining efficient power transmission (see Patent Document 1).